A common complaint of hearing aid users is that close-in sounds of interest and background sounds run together and cannot be distinguished from one another. Therefore, at cocktail parties, for example, the hearing aid user is often unable to carry on a conversation.
It is well known that persons with hearing loss, unlike persons with normal hearing, are often unable to unconsciously or consciously suppress background sounds. As such, what is unnoticeable to persons with normal hearing can be an irritating and annoying barrage to persons using hearing aids, especially hearing aids having automatic gain or level controls. This is so because the gain or level control circuits used are not designed to discriminate between close-in and background sounds. Both types of circuits operate to maintain specific output levels over a range of input sound levels. Often, the levels of sound present are large enough so that even the background sounds are amplified to near maximum output levels. As a result, the user's inability to discriminate between close-in and background sound is aggravated.
In the past, attempts have been made to remedy this bothersome phenomena. One method is to switch off the amplifying circuits of the hearing aid when sound pressure levels (SPL) fall below a predetermined threshold, and to switch the amplifier back on when the SPL exceeds the threshold. However, this method requires many circuit components, and involves the actual switching of amplifiers off and on.
Other attempts include logarithmic compression circuitry which produce adequate level controls, but minimal background sound compression effects, as well as require complex circuitry and many components.
In general, efforts have been directed toward controlling background sounds by directly modifying the automatic gain control circuits or amplifier circuits.
In the invention, background sound suppression circuity operates on the signal before any automatic level control circuitry or user volume control circuitry. The invention requires no direct amplifier gain manipulations nor any on/off switching. The background sound suppression circuitry, however, does interact with the automatic level control circuitry and user volume control circuitry to produce the novel and useful background sound suppression result.